This application is a U.S. national stage patent application of International Patent Application No. PCT/US14/72797, filed Dec. 30, 2014, the benefit of which is claimed and the disclosure of which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present disclosure relates generally to making measurements related to oil and gas exploration. More particularly, embodiments of the disclosure relate to systems and methods for measuring electromagnetic fields to detect a number of nearby wellbores, and to determine the locations of the nearby wellbores.
2. Background
In drilling wells for oil and gas exploration, understanding the structure and properties of the associated geological formation provides information to aid such exploration. In addition, drilling can be enhanced with systems and methods to detect conductive bodies below the earth's surface. The conductive bodies can include metal structures, e.g., casing and piping used in various down-hole operations, where the detection of the metal structures can reveal subterranean positions of existing wellbores. For example, the positions of existing wellbores can influence drilling operations in crowded fields where legal or land restrictions require wells to be drilled in close proximity with one another. In some instances, well avoidance is an important consideration in drilling in the crowded fields, and in some instances, well intersection can be intentional, e.g., for the repair of a damaged wellbore.
In other instances, determining the position of existing wellbores can facilitate drilling a wellbore in a predetermined relationship to the existing wellbore. For example, in steam assisted gravity drainage (SAGD) applications, a wellbore is often drilled parallel to existing wellbores. Generally in SAGD applications, steam is used in conjunction with two spaced apart wellbores (an SAGD pair) to address the mobility problem of heavy oil in a formation. High temperature steam may be injected into an upper wellbore (the injector), and used to heat the heavy oil to reduce its viscosity and thereby enhance the flow of the heavy oil into a lower wellbore (the producer) to enhance extraction of the heavy oil. Preferably, the injector and producer are drilled at a distance of only a few meters from one other, e.g., about 5 to about 15 meters. If the injector is positioned too close to the producer, the producer would be exposed to very high pressure and temperature and steam would be directly communicated to the producer. If the injector is positioned too far from the producer, the efficiency of the SAGD process is reduced. In order to assist in ensuring that the injector of an SAGD pair is positioned as desired relative to the producer wellbore, a survey of the geologic formation is often conducted. These surveying techniques are traditionally referred to as “ranging.” Often, these ranging techniques can be frustrated by the proximity of multiple nearby wellbores, e.g., where it can be difficult to distinguish magnetic fields contributed from a target wellbore from other nearby existing wellbores in a crowded field.